The digital television broadcast standard promulgated by the European Telecommunications Standards Institute (ETSI) includes both the digital video broadcast-handheld (DVB-H) standard and the digital video broadcast-terrestrial (DVB-T) standard. Those standards will be referred to herein collectively as the DVB standard. The DVB standard specifies various modulation and channel coding techniques to be used for digital television broadcasting. According to the DVB standard, MPEG-2 video streams are transmitted using digital modulation techniques known as Orthogonal Frequency Division Multiplexing (OFDM). In OFDM systems, the transmitted data modulates multiple subcarrier frequencies rather than a single carrier. Typical subcarrier modulation schemes include Bi-Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), or Quadrature Amplitude Modulation (QAM).
OFDM's parallel transmission of data over multiple simultaneous carriers provides a measure of protection against frequency-selective fading. Thus, while some carriers may be degraded, others will be unaffected. The portion of data transmitted on a given subcarrier is known as a “symbol,” and each symbol has a duration known as a “symbol period.” To reduce intersymbol interference, each modulation symbol period for each subcarrier is extended by a guard interval. Typically, the contents of the guard interval is a “cyclic prefix” of data repeated from the end of the active symbol period.
Before transmission, the MPEG-2 transport multiplex packets are scrambled, Reed-Solomon encoded, convolutionally byte-wise interleaved (outer interleaver), then convolutionally encoded. After convolution coding, the data is partitioned into v-bit sub-streams, and each sub-stream is bit- and symbol-interleaved, then mapped into the signal constellation.
On the receiver side, the received v-bit words are deinterleaved by symbol- and bit-deinterleavers. A Viterbi decoder corrects bit-wise errors, then the data stream is deinterleaved by a convolution deinterleaver. Byte-wise errors are corrected by a Reed-Solomon decoder. Finally a descrambler restores the original MPEG-2 transport multiplex packets.
Additional information regarding the DVB standard can be found in the literature including Laszlo Horvath et al, “A Novel, High-Speed Reconfigurable Demapper—Symbol Deinterleaver Architecture for DVB-T”, 1999 IEEE publication no. 0-7803-5471-0/99 and references cited therein. That paper purports to present a memory reduction technique in which the memory associated with the symbol de-interleaver is eliminated by optimizing for memory following the demapper. However, optimizing for memory following the de-mapper only solves a localized problem. It does not address the problem of the significant amount of memory space required for the overall demodulation function.